Milking device

ABSTRACT

A milking device for milking a dairy animal comprises a teat cup with a cup wall and a teat liner and a pulsation space situated in between, to which pulsation space a pulsation device is connected which is configured to apply a pressure that varies in pulsations to the pulsation space in order to open and close the teat liner, and which pulsation device comprises a supply line which is controllable by a first operable valve, in particular closable, for supplying a first pressure, a supply line which is controllable by a second operable valve, in particular closable, for supplying a second pressure, which is a lower pressure than the first pressure, and a control unit which is configured to generate control signals for operating the first valve and the second valve, wherein the first valve, and preferably also the second valve, is a controllable valve having a passage which is adjustable by means of the control signals, wherein the passage of the first valve, and preferably of the second valve, respectively, is adjustable during at least one pulsation phase by the control unit via the control signals.

This application is a continuation of U.S. Ser. No. 16/060,669 filedJun. 8, 2018, allowed, which is a 371 application of PCT/NL2016/050856filed Dec. 8, 2016 and claims the benefit of NL2015944 filed Dec. 11,2015. The contents of each of these applications are incorporated hereinby reference in their entirety.

The present invention relates to a milking device for milking a dairyanimal, and comprising a teat cup with a cup wall and a teat liner and apulsation space situated in between, to which pulsation space apulsation device is connected which is configured to apply a pressurethat varies in pulsations to the pulsation space in order to open andclose the teat liner.

Such automatic milking devices have been known in the prior art for along time. Thus, WO02/05629 describes a pulsator control with acontrollable pulsator valve for alternately connecting a vacuum sourceand ambient pressure to the pulsation space of a milking cup.

In practice, it has been found that a problem occurs with many knownpulsation devices and milking devices, with the teat liner suddenlyfolding at a certain value of said pressure and hitting the teat whenthe pulsation space is connected to the higher (ambient) pressure. Thisfolding, caused by the inherent elasticity of the teat liner, may causedamage and irritation to the teat, which is undesirable.

It is an object of the present invention to counteract said drawback, atleast partly, and to this end it provides a milking device according toclaim 1, in particular a milking device for milking a dairy animal, andcomprising a teat cup with a cup wall and a teat liner and a pulsationspace situated in between, to which pulsation space a pulsation deviceis connected which is configured to apply a pressure that varies inpulsations to the pulsation space in order to open and close the teatliner, and which pulsation device comprises a supply line for supplyinga first pressure, which supply line is controllable, in particularclosable, by a first operable valve, a supply line for supplying asecond pressure, which is a lower pressure than the first pressure,which supply line is controllable, in particular closable, by a secondoperable valve, and a control unit which is configured to generatecontrol signals for operating the first valve and the second valve,wherein the first valve, and preferably also the second valve, is acontrollable valve having a passage which is adjustable by means of thecontrol signals, wherein the passage of the first valve, and preferablyof the second valve, respectively, is adjustable during at least onepulsation phase by the control unit via the control signals.

It should be noted here that “adjustable passage” is understood to meanthat the passage is adjustable by the control device in at least oneintermediate position between a most open position and a most closedposition. In turn, “adjustable” means that the passage is activelydriven and controlled to a position corresponding to the controlsignals. With a known prior-art pulsator valve which can be controlledfrom a fully open position to a fully closed position and vice versa,all intermediate passage positions are obviously also assumed, but theseare not at all controlled or regulated and can therefore not serve as anadjustment parameter. Thus, the pulsator valve in WO02/05629 is onlyfully opened and closed on repeated occasions, which limits thepossibilities of adjustment and may, in addition, result in increasedwear, both of the valve itself, in particular the valve seats, and ofthe control unit.

The present invention offers the advantage that the control options forthe pulsator valve or even pulsator valves increase, resulting in morepossibilities of influencing the pressure course in the pulsation spaceduring a pulsation. In this way, more possibilities are provided inorder to counteract in particular the aforementioned drawbacks of theteat liner folding. Thus, it is for example possible to influence, inparticular reduce, the passage of the valve on the basis of acalibration or other measurements, just before the varying pressure inthe pulsation space reaches a value at which the teat liner will fold.Folding will thus occur much more slowly, which greatly reduces thestrain on the teats. All this will be explained in more detail below.

Further particular embodiments and examples are described in thedependent claims and the description of the figures, as well as in thedescription below.

In a first particular embodiment, the first and the second valve areeach a controllable valve having a passage which is adjustable by meansof control signals and the respective passages of the first valve andthe second valve are adjustable during at least one pulsation phase bythe control unit via the control signals. Thus, it is also possible toinfluence the pressure course inside the pulsation space favorablyduring other pulsation phases, in particular the phase in which a vacuumis produced in the pulsation space and in which folding occurs, but inthis case from a position bearing against the teat to the open position.

It should be noted in this case that, in the prior art, a pulsation isdivided into 4 phases, i.e. a, b, c, and d phases. In this case, the aphase is the phase in which the pressure in the pulsation space ischanged from atmospheric (or another starting pressure) to a pulsationvacuum (or another correspondingly lower pressure), which pressures arehere referred to as the first pressure and the second pressure,respectively. The b phase is the phase in which the lower pressureprevails in the pulsation space, which phase is also referred to as thesuction or milking phase. In the c phase, the pressure in the pulsationspace is returned to atmospheric (or another higher first pressure).Finally, the d phase is characterized by an atmospheric (or higher,first) pressure prevailing in the pulsation space, which d phase isreferred to as the rest stroke. The four phases may also becharacterized as follows: in the a phase, the teat liner opens, in the bphase, the teat liner is open, in the c phase, the teat liner closes, inthe d phase, the teat liner is closed, all this completely in accordancewith the prior art.

In embodiments, the passage of the first and/or of the second valve isadjustable in several intermediate positions by the control unit via thecontrol signals during a pulsation phase. This means that the passage ofthe respective valve(s) between the most open and most closed positionis furthermore adjustable in more than one intermediate position.Obviously, this increases the number of possibilities to influence thepressure course over time. In general, it will hold true that a largernumber of adjustable intermediate positions allows for greaterversatility in influencing the pressure course.

In particular, the passage of the first and/or of the second valve iscontinuously adjustable in several intermediate positions by the controlunit via the control signals during a pulsation phase. This provides amaximum influencing opportunity.

In embodiments, the pulsation has a usual a, b, c and d phase, and thepassage of the first and/or of the second valve during the c phaseand/or the a phase is adjustable by the control unit, via the controlsignals, in several intermediate positions with alternately enlarged andreduced passages. As has already been indicated above, the c phaserelates to the phase in which the teat liner will move from open toclosed and the a phase relates to the reverse movement from closed toopen. Since now, in addition, the passage can alternately be enlargedand reduced during a pulsation phase, the influencing opportunities areincreased still further. In particular, this may be seen in the case ofthe folding of the teat liner. During this folding, the volume of thepulsation space is changed by more than just the flow of air from or tothe pulsation space. This also means that the pressure course will showa ripple over time. This folding is caused by the elastic properties ofthe teat liner, wherein a mechanical resistance in the teat liner isovercome by the pressure difference across the teat liner. It could besaid that the folding and the associated change in volume causes anadditional air flow. In order to counteract the effect thereof, it isadvantageous to concomitantly change the airflow through the firstand/or second valve in a targeted manner. In order to counteract theusual ripple in the pressure course, it may be advantageous to make thepassage of the first and/or second valve smaller than before for a shorttime or, on the contrary, make the passage larger for a short time inorder then to continue with a larger or smaller passage, respectively.Obviously, more variations are also possible. Therefore, in particularembodiments the respective passages of the first valve and the secondvalve are alternately and/or repeatedly adjustable by the control unitvia the control signals during at least one pulsation phase. As a resultthereof, the influencing opportunities of the pressure course in thepulsation space are innumerable.

In particular embodiments, the respective passages of the first valveand the second valve are simultaneously adjustable by the control unitvia the control signals during at least one pulsation phase. In thiscase, it is thus possible for both valves to be in an open position atthe same time. It is also possible that a first one of the valves isopened first during a pulsation phase, is subsequently closed, followingwhich the other one of the valves is opened and closed again, stillduring the same pulsation phase, either completely or only partially, asdesired, etc. A significant advantage of these embodiments is that evenif the pressure in the pulsation space decreases (a phase) or increases(c phase), it may sometimes be favorable to partly counteract theassociated discharge or supply, respectively, of air. All this has, inparticular, a possible positive effect on the folding of the teat liner,which effects may be mitigated even more efficiently by a partlyopposite air flow.

In embodiments, at least one of the first and the second valve comprisesan electromagnetic valve. Such valves may comprise, for example, amagnetic or magnetizable valve body and a coil, which coil can generatean alternating and controllable elektromagnetic field to control thevalve body, and thus the valve(s). Such valves may be controlledaccurately and simply with regard to their passage. Nevertheless, othercontrollable valves are also possible, such as mechanically controlledbutterfly valves, etc.

In a particular embodiment, the milking device furthermore comprises apulsation pressure gauge for measuring a value of the pressure in thepulsation space and sending the measured pressure value to the controlunit, and the passage of the first and/or of the second valve isadjustable by the control unit via the control signals in dependence ofthe measured pressure value. Due to the fact that the pressure value inthe pulsation space can be measured with the pulsation pressure gaugeand can be sent to the control unit, the control unit can take it intoaccount and adjust the passage of the first and/or the second valve asdesired or to correspond with the measured pressure value. Thus, thepressure course in the pulsation space can be influenced efficiently. Itshould be noted here that any other sensor which can either measure avalue of a parameter representative for the pressure value or a sensorwhich can detect a position of the teat liner may alternatively be usedas a pulsation pressure gauge. Examples of such alternative sensors arean airflow sensor and a teat liner position sensor, such as anelectromagnetic sensor or a camera in the pulsation space or teat space.These alternative sensors can then also send a measured value or othersignal to the control unit, on the basis of which the control unit canadjust the passage of the first and/or second valve.

In embodiments, the control unit comprises a memory with a desiredpressure value in the pulsation space, in particular as a function oftime, wherein the control unit is furthermore programmed and configuredto compare the measured pressure value and the desired pressure value,in particular as a function of time, and wherein the passage of thefirst and/or of the second valve is furthermore adjustable by thecontrol unit via the control signals based on said comparison. With thisembodiment, a desired pulsation profile is stored in the memory, as itwere, with the control unit comparing the measured pressure value(“Istwert”) with the pressure value stored in the memory (“Sollwert”),respectively. In this case, it already suffices if such a comparison iscarried out at a fixed point in time during the pulsation, so that onepressure value in principle suffices. Obviously, a comparison at severalpoints in time and thus comprising several stored pressure values ismore accurate. All this may also depend on the speed with which thepressure gauge can be read out. It should be noted that in thisembodiment, as well as all subsequent embodiments, the pressure gaugeand the pressure values could be replaced and/or supplemented byalternative sensors and the associated parameter values.

The control unit may, for example, be efficiently configured to adjustthe passage of the first and/or of the second valve by means offeedback. In this case, the device may couple, for example, an errorvalue as difference value of the measured pressure and the desiredpressure to the associated control signals. By modifying the controlsignals based on the measured error, the error can be minimized in thesubsequent pulsations.

In embodiments, the control unit furthermore comprises a memory forstoring generated control signals associated with at least one appliedpulsation, wherein the control unit is furthermore configured togenerate control signals for the purpose of a new pulsation based onsaid comparison and on at least some of the stored control signals. Thisembodiment is suitable, for example, to perform the above-describedfeedback. Alternatively, it is also possible to configure the controlunit to generate the new control signals in an alternative way, inparticular on the basis of a non-causal model which is stored in thecontrol unit. This means, in particular, that the control unit isconfigured to change the passage of the first and/or the second valveeven before the desired pressure value has to change over time. In otherwords, the control unit is now configured to take into account a delayin the system, that is to say in the milking device. Since the pressurevalue is a direct consequence of moving volumes of air and said movementtakes time, there will often be a certain degree of delay regarding theeffects of modifying a passage. It is therefore advantageous if thedevice is configured to change the respective passage or passages beforean effect is to occur.

In embodiments, the memory comprises an animal-specific or groupwisepressure value, in particular as a function of time, and the milkingdevice comprises an animal recognition system which is operativelyconnected to the control unit. Thus, it is possible for the control unitto set the desired pulsation pressure value, or the desired pulsationprofile, for each animal or group of animals. For example, there areanimals with relatively sensitive teats which require a more gentlepulsation. There may also be differences with regard to milking speed,which may also produce differences in the desired pulsation profile.Advantageously, the memory comprises more than one pressure value(profile) which can be adjusted as a function of time for eachindividual animal or group of animals, wherein the device is configuredto select one of the stored profiles as a function of time on the basisof an additional milking parameter determined by the milking device. Tothis end, the milking device comprises suitable sensors, such as a milkflow sensor or the like. It should furthermore be noted here that theserecognition devices are generally known in the prior art.

In particular, the milking device furthermore comprises an input devicefor inputting or changing the desired pressure value, in particular as afunction of time, and more particularly for at least an animal or groupof animals. Such an input device may comprise, for example, a keyboard,internet connection, etc., wherein the desired pressure value or thedesired pulsation profile is actively changed by the user.Alternatively, the input device may also form part of the control unit,due to the fact that it makes a choice, based on an additional measuredmilking parameter, such as a milk flow, from the stored pressure valueor pulsation profiles in order thus to change the desired pressure valueor the desired pressure profile.

The invention also relates to a pulsation device for use in a milkingdevice according to the invention. Such a pulsation device is configuredto apply a pressure that varies in pulsations to the pulsation space ofa milking cup in order to open and close the teat liner of the teat cup,and comprises a supply line which is controllable by a first operablevalve, in particular closable, for supplying a first pressure, a supplyline which is controllable by a second operable valve, in particularclosable, for supplying a second pressure, which is a lower pressurethan the first pressure, and a control unit which is configured togenerate control signals for operating the first valve and the secondvalve, wherein the first valve, and preferably also the second valve, isa controllable valve having a passage which is adjustable by means ofthe control signals, wherein the passage of the first valve, andpreferably of the second valve, respectively, is adjustable during atleast a pulsation phase by the control unit via the control signals. Theadvantages of this pulsation device have already been described for themilking device and therefore do not have to be repeated here.

The milking device according to the invention furthermore comprises thecustomary components of milking devices, such as a vacuum source, forthe purpose of a milking vacuum and for the purpose of a pulsationvacuum, that is to say the lower second pressure, as well as milkinglines, a milking gauge, etc. Advantageously, the milking device is arobot milking device and then also comprises a robot arm for connectingthe teat cups to teats of a dairy animal, an animal recognition device,a teat recognition device. These components are outside the scope of thepresent invention and are furthermore known per se in the prior art.

The invention will be explained in more detail below with reference tothe attached drawing, which shows an exemplary embodiment of theinvention and in which:

FIG. 1 shows a diagrammatic view of a milking device according to theinvention,

FIG. 2 shows a standard graph of a pulsation profile,

FIG. 3 shows a graph of a desired pulsation profile and a commonpulsation profile, and

FIG. 4 shows a diagram with the desired pulsation profile from FIG. 3,an actual pulsation profile and valve passages as a function of time.

FIG. 1 shows a highly diagrammatic view of a milking device according tothe invention. The milking device 1 comprises a teat cup 2 with a cupwall 3 and a teat liner 4 and a pulsation space 5 in between. The teatliner 4 lines a teat space 6 for accommodating a teat of a dairy animal(not shown here), which teat space runs out into a milk discharge 7. Themilking device furthermore comprises a pulsation device which is denotedoverall by reference numeral 8 and which comprises a pulsation line 9, afirst operable valve 10 and a second operable valve 11 in, respectively,a supply line for ambient air 12 and a vacuum supply line 13, a pump 14,a pulsation pressure gauge 15 and a control unit 16 with a memory 17 andan input device 18. Reference numeral 19 denotes an animal recognitiondevice.

The teat cup 2 is a teat cup which is generally known per se and whereina pulsation is generated in the pulsation space 5 by means of thepulsation device 8. In this case, the teat liner 4 will be open when thepressure in the pulsation space is low (solid line) and will fold andclose the teat space 6 (dashed line) when the pressure is relativelyhigh, such as at ambient pressure.

The pressure in the pulsation space 5 which alternates for the purposeof pulsation is provided by operating, via the control unit 16, thefirst and second operable valves 10 and 11 which form a connection witha first pressure, usually ambient air, and a second, lower pressure,which is generated by means of the pump 14, respectively. The controlunit 16 generates operational control signals in order to operate thevalves 10 and 11.

More generally, the valves 10 and 11 are operable restrictions andcomprise, for example, electromagnetic valves or other ways of providinga different passage for the supply line 12 or 13, respectively.

The pulsation pressure gauge 15 measures the pressure in the pulsationspace 5 and sends a corresponding signal regarding the measured value tothe control unit 16. At least on the basis of the measured pressurevalue, the control unit 16 can emit suitable control signals to thevalves 10 and/or 11. The memory 17 may contain data on the basis ofwhich the control unit 16 can further determine the desired controlsignals. Such data contain, for example, a desired pulsation profile,control signals which have been generated previously and stored and/orpressure values of the pulsation gauge 15. Furthermore, by means of theinput device 18, the memory 17 may be provided with new or otherinformation, such as a change in the desired pulsation profile, data ofnew animals and/or groups of animals, etc. In this case, the inputdevice 18 may comprise a keyboard, a disk drive, an internet connection,etc.

Reference numeral 19 denotes an animal recognition device forrecognizing animals to be milked by the milking device 1. Such an animalrecognition device comprises, for example, a so-called tag reader, whichis generally known in the prior art. Details of such an animalrecognition device are not important for the device as such. By means ofthe animal recognition device, it is possible to determine the identityand to send it to the control unit 16 which can in turn retrieve theassociated animal and pulsation data and the like from the memory 17.

The action of a pulsator can be explained in more detail as follows.With prior-art pulsators, the single pulsator valve or in some caseseach pulsator valve is operated in a position which alternates betweenfully open and completely closed. This means that no further control canbe exerted in the airflows from and to the pulsation space 5. With thepresent invention, the passage of at least the first valve 10 and, inparticular embodiments, also of the second valve 11 can be controlled bycontrol signals from the control unit 16. By suitably varying thepassage of the one or two valves, the airflow to, and in particular alsofrom, the pulsation space 5 can be controlled even better. Thiscounteracts in particular the drawbacks of the folding of the teat liner4 from the open to the closed position, as a result of which a teatwhich is accommodated in the teat space 6 is subjected to less stress.

FIG. 2 shows an idealized pulsation profile, with time being shown onthe X axis in relative units or in seconds if a pulsation lasts exactly1 second, which is not unusual. The Y axis shows the absolute pressurein the pulsation space in kPa. In this pulsation profile, movement ofthe teat liner is not taken into account, in particular no foldingthereof or any other “spontaneous” change in volume. Furthermore, it isbased on the premise that an ‘open/closed’ valve control unit of apulsation device is used, so that the pressure difference is graduallyand smoothly reduced.

The pulsation profile comprises the four standard phases a, b, c and d.For this pulsation profile, the milking vacuum in the teat space hasbeen assumed to be 40 kPa, so that the absolute pressure in this teatspace is in principle 60 kPa. For the phase transitions between the 4phases, use has been made in this case of the standard 10 percent of thepressure difference, so that the transition from c to d and from d to atakes place at 96 kPa. Furthermore, the pulsation vacuum has been set ata value of 56 kPa, so that the transition from a to b and from b to atakes place at 60 kPa.

FIG. 3 shows a diagram with both an actual practical pulsation profile(solid line) and an alternative desired pulsation profile (dashed line).

The solid line is a representation of a pulsation profile which willoccur in practice with a prior-art milking device when the pulsationdevice is controlled in an “open/closed” fashion. The theoreticalpulsation profile of FIG. 2 then changes into, for example, theillustrated pulsation profile occurring in practice, where the effect ofthe folding of the teat liner can be seen as a ripple at a pressurevalue around 65 kPa in the falling section and around a pressure valueof 70 kPa in the rising section of the pulsation profile. In particular,the quick folding in the rising section of the pulsation profile isundesired and may be prevented by means of the present invention. Tothis end, it is expedient for the pulsation profile to be much slowerparticularly around the pressure value at which folding takes place.This can be seen in the diagram by the fact that the pressure in thedesired pulsation profile rises much more slowly around a value of 70kPa. By contrast, in this theoretical pulsation profile, it has beendecided to opt for a decrease in pressure which is as quick as possibleas the desired course when opening the teat liner.

In order to achieve the desired pulsation profile in practice, thecontrol unit will have to perform a different actuation of the one ormore pulsation valves than an “open/close” control.

FIG. 4 shows an example of how the first valve 10 from FIG. 1 and thesecond valve 11 are actuated to achieve the desired pulsation profile tothe greatest possible degree. The top part of the diagram shows aportion of the desired pulsation profile; more specifically the risingsection (dashed line) and the pulsation pressure measured in practice atthe given control signals (solid line). The central part of the diagramshow the passage of the first valve 10 with the same time axis, inrelative units, and the bottom part shows the passage of the secondvalve 11.

It can be seen that the first valve 10 is opened for a short time beforethe desired rise in pressure and then closed again, and an irregularcurve shows the corresponding irregular and partial opening and closingof the valve, up to approximately t=0.73, after which the valve is thenopened completely. It can clearly be seen that periods where the valveopens further and less far alternate, and that various intermediatepositions between a fully closed and a fully open position are actuated.It can be seen that the pulsation pressure rises from the lowest to thehighest position in approximately 0.12 seconds, whereas this takes placein approximately 0.10 seconds in the practical pulsation from FIG. 3. Bycontrast, the folding in the last-mentioned profile takes place in a fewhundredths of seconds, whereas this period of time is at least threetimes as long according to the currently measured profile in FIG. 4.This also means that folding proceeds significantly more slowly andtherefore more gently.

The bottom diagram shows a passage of the second valve 11 as a functionof time. It should be noted that it is also repeatedly actuated and indifferent passage positions, alternately larger and smaller. It shouldfurthermore be noted here that this embodiment, in which both valves areoperated simultaneously in a single phase of the pulsation, may have afurther positive effect on, for example, the air flow and the folding ofthe teat liner, if part of any surplus of air flowing in can be capturedby opening the second valve to the vacuum supply line. Conversely, theair supply to the teat space can be controlled better by slightlyopening the vacuum supply via the second valve during the c phase inprinciple as standard, in which case the net air supply to the teatspace can be increased by (temporarily) closing the second valve. Itwill be clear that the present invention further increases thepossibilities of influencing the air supply from and to the teat space,and thus the pulsation pressure and the folding of the teat liner. Anadvantage of such a kind of actuation is that it is in turn possible toreduce the pressure in the pulsation space, or at least to prevent anincrease thereof. For example, the folding of the teat liner may beslowed down by temporarily sucking air from the pulsation space again atthat point in time. Other combinations are also conceivable, and itshould furthermore be noted that it is not necessary to operate bothvalves simultaneously, but that the advantage of the invention can oftenalso be achieved by means of the described control unit with a singlevalve.

The passage of the first valve 10 and/or the second valve 11 illustratedin FIG. 4 can simply be brought about by actuating an electromagneticcoil in an electromagnetic embodiment of the respective valve 10, 11 bymeans of a corresponding electrical signal, in particular a currentsignal. This current signal will generate a corresponding strongmagnetic field which will attract a magnetizable valve body in the valveto a greater or lesser degree, and accordingly control the passage ofthe valve. Obviously, there are other possible ways of controlling thevalve position and thus the passage, in which case it should again benoted that “valve” in each case is to be understood as referring to thewider concept of “restriction”. In case a restriction has a non-linearactuation, the control unit obviously has to be adapted in acorresponding manner.

It should be noted that, in the case of feedback control, the valvecannot be actuated before the measured pressure rises, since there is nochange in pressure yet. Precisely by starting to actuate the valveearlier according to this embodiment, and thus opening it, the delaytime of air displacement in the system can be compensated forefficiently.

By means of the measured pressure values, either as a profile or as oneor more pressure values over the course thereof, the control unit canfurthermore improve control. In this case, the control unit compares themeasured values to the desired profile, or the corresponding values inthat profile, and looks at the difference or margin of error. If themeasured pressure value is too high, the control unit can reduce thepassage of the valve and vice versa. In this way, the control unit is inprinciple able to come increasingly closer to the desired profile. Inthis case, the control unit is advantageously configured to use theprevious control signals, which may be stored in the memory, and themeasured pressure signals.

The illustrated and described exemplary embodiments are not intended tobe limiting, but only serve as an explanation of the invention, thescope of protection of which is determined by the attached claims.

1. A milking device for milking a dairy animal, and comprising a teatcup with a cup wall and a teat liner and a pulsation space situated inbetween, to which pulsation space a pulsation device is connected whichis configured to apply a pressure that varies in pulsations to thepulsation space in order to open and close the teat liner, and whichpulsation device comprises: a supply line for supplying a firstpressure, which supply line is controllable, in particular closable, bya first operable valve, a supply line for supplying a second pressure,which is a lower pressure than the first pressure, which supply line iscontrollable, in particular closable, by a second operable valve, and acontrol unit which is configured to generate control signals foroperating the first valve and the second valve, wherein the first valve,and preferably also the second valve, is a controllable valve having apassage which is adjustable by means of the control signals, wherein thepassage of the first valve, and preferably of the second valve,respectively, is adjustable during at least one pulsation phase by thecontrol unit via the control signals.